The present invention relates to aqueous compositions for the wet-end treatment of cellulose fibres/fibrilles for the manufacture of paper having oleo-repellence properties.
More specifically the invention relates to aqueous compositions based on fluorinated products capable to confer to paper an oleo-repellence capable to pass the application tests required by the manufacturers of oleo-repellent articles (grease-proof test) for the food or pet-food industry.
It is well known that the paper is used for the packaging of fats based on vegetable oils, of products as coffee, chocolate and also for the packaging of foods having a high fat content as meats, chips, hamburgers, popcorns, foods to be cooked in microwave ovens, and pet food. For said uses it is necessary that the paper be treated with products capable to confer resistance to oils and greases.
The oleo-repellence is commonly evaluated in terms of resistance of the paper sized to the penetration of the oil contained in hydrocarbon drops or hydrocarbon mixtures having a progressively decreasing surface tension, maintained for 15 seconds in contact with the paper specimen (Kit Test, TAPPI 557 method). Usually drops consisting of mixtures of castor oil, toluene and heptane in various ratios are used. The oleo-repellence values obtained with the Kit Test are however an index of the only surface activity of the fluorinated additive and often they have a poor correlation with the real performance in terms of protective barrier to oils and fats, both in normal utilization conditions of the paper packages in which there are prolonged contact times with foods, and in severe utilization conditions due to the temperature (heating of the food packages in microwave ovens) and mechanical stresses due to the bending to obtain the mnanufactured article. On this ground users utilize a series of tests considered more adherent to practical applications such for example:
Ralston Crease Test (RP-2 test): The resistance properties to the oil penetration in greaseproof papers for pet-food packaging are evaluated. The percentage of the surface of the paper stained by the coloured oil is determined. The specimen acceptability limit threshold is 2% of stained surface.
Resistance test to oleic acid: The resistance to oleic acid is evaluated at 60xc2x0 C. for two hours. The test is passed when the paper is not stained and it does not show halos (% of stained surface=0).
Resistance test to fat acid mixtures: The resistance to a mixture of palmitic/lauric fat acids (C16/C12) is evaluated at 65xc2x0 C. for 5 minutes. The test is passed when the paper is not stained and it does not show halos.
See the examples for the detailed description of said tests.
Compositions to confer oleo-repellent properties to the already formed paper are known in the prior art. However it is well known that the compositions used for said treatments are not necessarily effective when used for wet-end applications. In fact when said compositions are added to the paper slurry, to confer oleo-repellence they must be uniformly adsorbed on the paper fibrilles, which not always happens since said compositions can interact with the various additives present in the paper slurry, such for example polymer retention agents.
Known oleo-repellent compositions contain fluorinated components among which phosphates containing perfluoroalkyl groups, polymers containing pendent perfluoroalkanes with respect to the backbone and/or derivatives thereof in the presence of surfactants having a perfluoroalkyl chain (for example U.S. Pat. No. 5,271,806) can be mentioned. Said commercially used components contain perfluoroalkyl segments which by degradation give rise to perfluorooctyl components to be avoided since they tend to bioaccumulate. See for example patent WO 01/30873.
In U.S. Pat. No. 6,221,434 the use of (per)fluoropolyether phosphoric mono- or diesters for the paper surface sizing to confer oleo-repellence is described. According to the examples said components are used, also in salified form with NH4OH, in an aqueous solution containing isopropyl alcohol in a weight ratio 4:1 and 10:1 with respect to the component, in which the paper is dipped. In this patent no mention is made to the use of said components for their wet-end application of the paper. Tests carried out by the Applicant in the paper wet-end application using said compounds in aqueous solution containing isopropanol in a weight ratio with said compounds 4:1 have shown that said components are unable to confer satisfactory oleo-repellence values to pass the application tests required in the food industry (see the comparative Examples).
The need was therefore felt to have available aqueous compositions which in the wet-end applications conferred to paper an oleo-repellence capable to pass the most severe performance tests, such as those of resistance to oleic acid and to fat acid mixtures.
The Applicant has unexpectedly and surprisingly found specific aqueous compositions based on (per)fluoropolyether phosphates capable to satisfy the above mentioned requirements.
An object of the present invention are aqueous compositions comprising the following components:
I) a phosphate selected from the following
Txe2x80x94Oxe2x80x94[Rfxe2x80x94CFYxe2x80x94Lxe2x80x94O]P(O)(Oxe2x88x92Z+)(OH)xe2x80x83xe2x80x83(A)
(OH)m(Oxe2x88x92Z+)2-mP(O)[Oxe2x80x94Lxe2x80x94YFCxe2x80x94Oxe2x80x94Rfxe2x80x94CFYxe2x80x94Lxe2x80x94Oxe2x80x94P(O)(Oxe2x88x92Z+)]mxe2x80x2xe2x80x94[Oxe2x80x94Lxe2x80x94YFCxe2x80x94Oxe2x80x94Rfxe2x80x94CFYxe2x80x94Lxe2x80x94O]P(O)(Oxe2x88x92Z+)2-m(OH)mxe2x80x83xe2x80x83(B)
or mixtures of A) and B)
wherein
mxe2x80x2 is an integer from 0 to 20, preferably from 0 to 4;
L is an organic group selected from xe2x80x94CH2xe2x80x94(OCH2CH2)nxe2x80x94, xe2x80x94COxe2x80x94NRxe2x80x2xe2x80x94(CH2)qxe2x80x94, with Rxe2x80x2=H or C1-C4 alkyl; n is a number from 0 to 8, preferably from 1 to 3; q is a number from 1 to 8, preferably from 1 to 3;
Z+=alkaline metal ion or a NR4 group with R=H or C1-C4 alkyl or an aliphatic amine ion;
Y=F, CF3;
m is a number between 0 and 1, extremes included;
Rf is a (per)fluoropolyoxyalkylene chain having a number average molecular weight between 350 and 8,000, preferably between 500 and 3,000, formed by repeating units, statistically distributed along the chain, having at least one of the following structures:
(CFXO), (CF2CF2O), (CF2CF2CF2O), (CF2CF2CF2CF2O), (CR4R5CF2CF2O), (CF(CF3)CF2O), (CF2CF(CF3)O),
wherein
X=F, CF3;
R4 and R5, equal to or different from each other, are selected from H, Cl, or perfluoroalkyl from 1 to 4 carbon atoms;
T is a (per)fluoroalkyl group selected from xe2x80x94CF3, xe2x80x94C2F5, xe2x80x94C3F7, xe2x80x94CF2Cl, xe2x80x94C2F4Cl, xe2x80x94C3F6Cl, optionally substituted with one or two H atoms, preferably one, at the place of F atoms; and
II) a solvent selected from C1-C5 aliphatic alcohols, preferably isobutanol, aliphatic and cyclic ethers, preferably tetrahydrofuran, aliphatic acetates and mixtures thereof
wherein the ratio by weight between components I and II is in the range 1:1-1:0.05, preferably 1:0.5-1:0.1.
When component I) having formula (B) is used, mixtures of components B) wherein mxe2x80x2 is different from 0, preferably 1, can be used with components B) wherein mxe2x80x2=0, in a molar ratio in the range 5:95-50:50.
In particular Rf in the (A) and (B) structures can have one of the following structures:
1) xe2x80x94(CF2O)axe2x80x2xe2x80x94(CF2CF2O)bxe2x80x2xe2x80x94
with axe2x80x2/bxe2x80x2 comprised between 0.5 and 2, extremes included, axe2x80x2 and bxe2x80x2 being integers such to give the above mentioned molecular weight;
2) xe2x80x94(C3F6O)rxe2x80x94(C2F4O)bxe2x80x94(CFXO)txe2x80x94
with r/b=0.5-2.0; (r+b)/t is in the range 10-30,
b, r and t being integers such to give the above mentioned molecular weight, X has the above indicated meaning;
3) xe2x80x94(C3F6O)rxe2x80x2xe2x80x94(CFXO)txe2x80x2xe2x80x94
txe2x80x2 can be 0;
when txe2x80x2 is different from 0 then rxe2x80x2/txe2x80x2=10-30,
rxe2x80x2 and txe2x80x2 being integers such to give the above mentioned molecular weight; X has the above indicated meaning;
4) xe2x80x94(OCF2CF(CF3))zxe2x80x94OCF2(Rxe2x80x2f)yxe2x80x94CF2Oxe2x80x94(CF(CF3)CF2O)zxe2x80x94
wherein z is an integer such that the molecular weight be that above mentioned;
y is an integer comprised between 0 and 1 and Rxe2x80x2f is a fluoroalkylene group for example from 1 to 4 carbon atoms;
5) xe2x80x94(OCF2CF2CR4R5)qxe2x80x94OCF2(Rxe2x80x2f)yxe2x80x94CF2Oxe2x80x94(CR4R5CF2CF2O)sxe2x80x94
wherein:
q and s are integers such that the molecular weight be that above mentioned;
R4, R5, Rxe2x80x2f, y have the above indicated meaning;
6) xe2x80x94(C3F6O)rxe2x80x3(CFXO)txe2x80x3xe2x80x94OCF2(Rxe2x80x2f)yxe2x80x94CF2O(CF(CF3)CF2O)rxe2x80x3(CFXO)txe2x80x3xe2x80x94
wherein rxe2x80x3/txe2x80x3=10-30,
rxe2x80x3 and txe2x80x3 being integers such to give the above mentioned molecular weight; Rxe2x80x2f and y having the above indicated meaning.
The monofunctional and bifunctional (per)fluoropolyoxyalkylenes can be prepared starting from the corresponding (per)fluoropolyoxyalkylenes having xe2x80x94COF end groups (see for example patents GB 1,104,482, U.S. Pat. Nos. 3,715,378, 3,242,218, 4,647,413, EP 148,482, U.S. Pat. No. 4,523,039, EP 340,740, WO 90/03357, U.S. Pat. No. 3,810,874, EP 239,123, U.S. Pat. Nos. 5,149,842, 5,258,110).
The invention compositions are prepared by adding to the phosphates corresponding to component I) wherein Z+=H+, an amount of solvent II) in the ratios above mentioned for components I) and II), an aqueous solution of a base until reaching a pH in the range 7-10. Preferably the base is selected between ammonia and triethanolamine.
The invention compositions are prepared as concentrates containing 20-25% by weight of phosphates I), component II) is in the above mentioned ratio, the complement to 100% by weight is water. Said compositions can be subsequently diluted with water at the application time, preferably containing 0.1-5% by weight of phosphate I) with respect to the dry cellulose. Said compositions diluted for the wet-end application show an average size of the aggregates of the phosphate I) lower than 150 nm, determined by Dynamic Laser Light Scattering (DLLS).
The wet-end process consists in the paper formation starting from a cellulose slurry in water. The slurry can be formed or by virgin soft wood or hard wood, obtained by Kraft and/or sulphite process, suitably refined, or by recycled cellulose slurries or also by mixtures of said two kinds of slurries. The dry cellulose concentration in the slurry ranges from 0.1% to 10% by weight. The pulp-slurry can contain the additives normally used in the paper industry, for example organic or inorganic fillers, such as talc, kaolin, calcium carbonate or titanium dioxide; supporting agents as starches, dextrins, retention agents, flocculating agents, buffer systems, fungicides, biocides, sequestrants, gluing agents such as ASA (alkenyl succinic anhydride) or AKD (alkyl ketene dimer). The cellulose suspension can have both acid and basic pH, preferably basic.
The invention compositions are generally added to the aqueous cellulose slurry in an amount such to obtain paper having a phosphate I) content in the range 0.1%-5% by weight with respect to the cellulose dry content.
To improve the phosphate retention on the cellulose fibers, it is preferable to add to the pulp-slurry a fixative agent, before adding the phosphate. Said fixative agent is generally a cationic compound, often of polymer nature, having a molecular weight ranging from 10,000 to 5,000,000, in an amount ranging from 0.01% to 1% by weight of cationic compound based on the dry cellulose. The fixative agents are for example the following: cationic polyacrylamides, polyamines, polyamidoamine-epichlorohydrin or dimethylamine-epichlorohydrin copolymers, polyethylenimines, polydially-dimethyl-ammonium chloride. To the pulp-slurry chelants can be added to moderate the water hardness.
After addition of the phosphate to the cellulose slurry, the water is removed obtaining a wet paper which is dried, for example, at temperatures in the range 90xc2x0 C.-130xc2x0 C., according to the standard procedures used in the paper industry.
The preparation of the (per)fluoropolyether phosphates I) can be carried out as follows. The structure (A) monofunctional phosphates can be prepared by reacting the corresponding (per)fluoroalkylenoxides hydroxy-ended with POCl3. To obtain compound A) it is necessary to use a molar ratio POCl3/hydroxy-ended compound in the range 2/1-10/1, preferably 6/1-8/1. The reaction is carried out by slowly dropping the hydroxy-ended compound in POCl3, at a temperature between 50xc2x0 and 100xc2x0 C., preferably between 70xc2x0 and 80xc2x0 C., by removing the HCl vapours in a KOH trap. The POCl3 excess is removed by distillation while the formed adduct is hydrolyzed by H2O. The obtained product separation takes place by extraction with a suitable organic solvent, such for example ethyl acetate.
The structure (A) product is separated from the organic phase according to known techniques, for example by solvent evaporation.
The structure (B) bifunctional (per)fluoropolyether phosphates preparation can be carried out by reacting the corresponding (per)fluoroalkylenoxides di-hydroxy-ended with POCl3. To obtain the derivative with mxe2x80x2=0, it is necessary to use a molar ratio POCl3/di-hydroxy-ended compound comprised between 4/1 and 20/1, preferably between 12/1 and 16/1. The reaction is carried out by slowly dropping the hydroxy-ended compound in POCl3, at a temperature in the range 50xc2x0-100xc2x0 C., preferably 70xc2x0-80xc2x0 C., by eliminating the HCl vapours in a KOH trap. The POCl3 excess is removed by distillation while the formed adduct is hydrolyzed by H2O. The separation of the product (B) with mxe2x80x2=0 takes place by extraction with a suitable organic solvent, such for example ethyl acetate. From the organic phase the product is separated according to known techniques, for example by solvent evaporation.
To obtain the product of structure (B) with mxe2x80x2 greater than 0, one proceeds as in the case mxe2x80x2=0 with the difference that after the POCl3 removal, the reaction adduct is further reacted with variable amounts of di-hydroxy-ended compound. Subsequently hydrolysis is carried out and the above described techniques is performed.
A further object of the present invention is the use of the above described aqueous compositions as additives of the pulp-slurry based on cellulose fibers (wet-end) to obtain oleo-repellent paper.
The following Examples are given for illustrative but not limitative purposes of the invention.